The present invention generally relates to a turbomachine and, more particularly, to a system and apparatus that restricts oil transfer from rotating component sumps into the annulus between the rotor shafts of a turbomachine.
A turbomachine may include rotating components such as a fan, a compressor, and a turbine. A rotor shaft clamps the rotating components, forming a rotor group. Two or more bearing assemblies support the rotor group. The bearing assemblies are surrounded by support housings connected to the engine case. Various sealing apparatus are used to retain oil within the bearing compartments.
Some turbomachines include two or more coaxial rotor shafts, for example a high pressure turbine (HPT) shaft and a low pressure turbine (LPT) shaft. Oil from a rotating component sump may enter the annulus between the shafts, resulting in coked oil build up on the inner diameter (ID) of the outer shaft and on the outer diameter (OD) of the inner shaft. Because the shafts are rotating, the coked oil build up on the ID of the outer shaft can rub the OD of the inner shaft resulting in the cutting of the inner shaft. The shaft in-situ machining can lead to a cut/separated shaft and an engine in flight shut down. For some applications, the coked oil build up is due to air pressure differentials between the two rotating component sumps and further exasperated by high operating and soak back temperatures. Various sealing apparatus have been used to restrict oil passage and reduce coked oil build up.
U.S. Pat. No. 4,754,983 provides a sealing system for a gas turbine engine. The system includes two rings surrounding the inner shaft. The rings are pivotally connected to a housing mounted on the outer shaft. The pivot axes of the rings are 180° apart from each other. Under the action of centrifugal force during rotation of the outer shaft, the rings pivot laterally towards the surfaces of the housing to take up outer circumferential clearances. The described sealing system may restrict oil passage at the forward end of the annulus between the shafts. For some applications, a means to restrict oil passage at the exit (aft end) of the annulus is also needed. Additionally, the described system does not provide a means to purge the oil should it enter the annulus.
U.S. Pat. No. 5,211,535 provides a labyrinth seal for a gas turbine engine. The described seal includes a cylindrical sleeve and a plurality of annular seal teeth. The sleeve is attached to and distinct from the outer shaft, which prevents stress cracks created in the region of the seal teeth from propagating to the outer shaft. The seal teeth extend radially inwardly to the inner shaft, forcing fluid trapped in the seal along the inner shaft. Although the sleeve may facilitate seal maintenance and the teeth may improve seal efficiency for some applications, the described seal has high air leakage and does not provide a means to restrict oil passage at the exit of the annulus.
As can be seen, there is a need for an improved sealing system for restricting oil passage into the annulus between two shafts. Additionally, a system is needed that provides a means to purge oil from the annulus should oil enter the annulus.